Lumiphoric materials are commonly used with electrically activated emitters to produce a variety of emissions such as colored (e.g., non-white) or white light (e.g., perceived as being white or near-white). Such emitters may include any device capable of producing visible or near visible (e.g., from infrared to ultraviolet) wavelength radiation including, but not limited to, xenon lamps, mercury lamps, sodium lamps, incandescent lamps, and solid state emitters—including light emitting diodes (LEDs), organic light emitting diodes (OLEDs), polymer light emitting diodes (PLEDs), light emitting polymers, and lasers. Electrically activated emitters may have associated filters that alter the color of the light and/or include lumiphoric materials that absorb a portion of a first peak wavelength emitted by the emitter and re-emit the light at a second peak wavelength different from the first peak wavelength. Examples of common lumiphoric materials include, but are not limited to, phosphors, scintillators, and lumiphoric inks.
LEDs are solid state electrically activated emitters that convert electric energy to light, and generally include one or more active layers of semiconductor material sandwiched between oppositely doped layers. When bias is applied across doped layers, holes and electrons are injected into one or more active layers, where they recombine to generate light that is emitted from the device. Laser diodes are solid state emitters that operate according to similar principles.
Solid state light sources may be utilized to provide colored (e.g., non-white) or white light (e.g., perceived as being white or near-white). White solid state emitters have been investigated as potential replacements for white incandescent or fluorescent lamps due to reasons including substantially increased efficiency and longevity. Longevity of solid state emitters is of particular benefit in environments where access is difficult and/or where change-out costs are extremely high. A representative example of a white LED lamp includes a package of a blue LED chip (e.g., made of InGaN and/or GaN) combined with a lumiphoric material such as a phosphor (typically YAG:Ce) that absorbs at least a portion of the blue light (first wavelength) and re-emits yellow light (second wavelength), with the combined yellow and blue emissions providing light that is perceived as white or near-white in character. If the combined yellow and blue light is perceived as yellow or green, it can be referred to as ‘blue shifted yellow’ (“BSY”) light or ‘blue shifted green’ (“BSG”) light. Addition of red spectral output from an electrically activated emitter or lumiphoric material may be used to increase the warmth of the aggregated light output. Additional or different supplemental electrically activated emitters and/or lumiphors of different wavelengths may be provided to provide desired spectral response. As an alternative to phosphor-based white LEDs, combined emission of red, blue, and green emitters and/or lumiphoric materials may also be perceived as white or near-white in character. Another approach for producing white light is to stimulate phosphors or dyes of multiple colors with a violet or ultraviolet LED source.
In contrast to sunlight, and also in contrast to standard incandescent and halogen lamps, individual solid state emitters such as LEDs typically emit relatively narrow ranges of wavelengths. For example, each “pure color” red, green, and blue diode typically has a full-width half-maximum (FWHM) wavelength range of from about 15 nm to about 30 nm. Substantial efforts have been undertaken to broaden spectral output of devices including solid state emitters (such as by mixing light from many LEDs having different chromaticities and/or using one or more phosphors) in order to increase efficacy in general illumination applications, and to better emulate spectral power distribution characteristic of an incandescent or halogen emitter. For instance, emissions from a LED/phosphor combination that would otherwise be cool white and deficient in red component (e.g., compared to an incandescent emitter) may be supplemented with red and/or cyan LEDs, such as disclosed by U.S. Pat. No. 7,095,056 (Vitta), to achieve a desired color temperature and provide generally warmer light.
Many modern lighting applications require high power emitters to provide a desired level of brightness. High power emitters can draw large currents, thereby generating significant amounts of heat. Conventional binding media used to deposit lumiphoric materials such as phosphors onto emitter surfaces typically degrade and change (e.g., darken) in color with exposure to intense heat. Degradation of the medium binding a phosphor to an emitter surface shortens the life of the emitter structure. When the binding medium darkens as a result of intense heat, the change in color has the potential to alter its light transmission characteristics, thereby resulting in a non-optimal emission spectrum. Limitations associated with binding a phosphor to an emitter surface generally restrict the total amount of radiance that can be applied to a phosphor. In order to increase reliability and prolong useful service life of a lighting device including a lumiphoric material, the lumiphoric material may be physically separated from an electrically activated emitter.
U.S. Pat. No. 7,070,300 to Harbers et al. discloses various arrangements of phosphor layers that are physically separated from one or more electrically activated light sources, permitting the light source(s) to be driven with increased current to produce higher radiance without thermal degradation of the phosphor layers. In each instance, Harbers discloses transmission of light though phosphor layers (for wavelength conversion) before the resulting emissions exit the device. The requirement that all emissions be transmitted through phosphor layers in a device according to Harbers limits the concentration and/or amount of phosphor material that may be used, however, since an excessive concentration and/or amount of phosphor material would unduly attenuate or even block light emissions from exiting the device. It would be desirable to enable greater concentrations and/or amounts of phosphor materials to be used in lighting devices without unduly attenuating or blocking emissions from exiting a lighting device.
U.S. Patent Application Publication No. 2010/0103678 to van de Ven, et al. discloses a lighting device that includes at least one centrally located, rear-facing electrically activated solid state emitter (optionally including one or more lumiphoric materials arranged thereon) arranged to emit light toward a reflector that reflects light forward for transmission past (e.g., around) the solid state emitter(s) to exit the lighting device in a forward direction. The electrically activated emitter(s) are arranged in thermal communication with a heat pipe that conducts heat from the electrically activated emitter(s) to a heatsink arranged along a lateral periphery of the lighting device to provide adequate heat dissipation. Although providing rear-facing electrically activated solid state emitters remotely located from a reflector provides favorable optical characteristics (e.g., reduced glare and/or controlled beam angle), devices according to van de Ven are expensive to manufacture due to the necessary inclusion of a heat pipe, and further exhibit various limitations associated with placing lumiphoric materials in conductive thermal communication with electrically activated emitters (as outlined hereinabove). It would be desirable to provide lighting devices with favorable optical and heat transfer characteristics, while eliminating the need for heatpipes and permitting the use of remote lumiphoric materials.
It would be desirable to provide lighting devices including lumiphor-converted emissions and capable of operating at high luminous flux, including emissions with high color rendering index and color quality scale characteristics. It would further be desirable to provide lighting devices with readily adjustable output color and/or chromaticity. It would also be desirable to provide lighting devices with adjustable focus, adjustable beam pattern, and/or adjustable color mixing characteristics.
Various embodiments as disclosed herein address or more of the foregoing concerns.